This publication fills an important knowledge gap by providing guidance on how to assess contextual drivers of social accountability effectiveness. It aims to strategically support citizen engagement at the country level and for a specific issue or problem. The report proposes a novel framing of social accountability as the interplay of constitutive elements: citizen action and state action, supported by three enabling levers: civic mobilization, interface and information. For each of these constitutive elements, the report identifies 'drivers' of contextual effectiveness which take into account a broad range of contextual factors (e.g., social, political and intervention-based, including information and communication technologies). Opening the Black Box offers detailed guidance on how to assess each driver. It also applies the framework at two levels. At the country level, the report looks at 'archetypes' of challenging country contexts, such as regimes with no formal space or full support for citizen-state engagement and fragile and conflict-affected situations. The report also illustrates the use of the framework to analyze specific social accountability interventions through four case studies: Sierra Leone, Pakistan, Yemen, and the Kyrgyz Republic.